The present invention relates to a sheet reversing apparatus for a sheet-fed rotary press with a reversing mechanism, which has upstream and downstream cylinders with respect to a paper convey direction and a paper convey cylinder disposed therebetween to be in contact with each other and reverses a paper sheet upon gripping and conveyance of the paper sheet between the upstream cylinder and the paper convey cylinder, thereby performing perfecting printing.
Various sheet-fed rotary presses with reversing mechanisms each capable of performing single-sided printing and perfecting printing have been proposed and put into practice along with a variety of printing techniques. An example of such a rotary press is disclosed in U.S. Pat. No. 4,448,125. This rotary press has double-diameter impression cylinders on the upstream and downstream with respect to a paper convey direction and a reversing cylinder disposed therebetween to serve as a double-diameter paper convey cylinder. This apparatus will be described below.
FIGS. 18 to 23 show a sheet-fed rotary press with a reversing mechanism disclosed in this prior art. FIG. 18 shows the cylinder arrangement. FIG. 19 shows a paper holding unit and a paper trailing end holding unit. FIG. 20 corresponds to FIG. 19 and shows the paper holding unit and the paper trailing end holding unit in a state wherein the paper trailing end holding unit holds the trailing end of a paper sheet to transfer the paper sheet to the paper holding unit. FIG. 21 shows the cylinder arrangement for a single-sided printing operation. FIGS. 22 to 24 show the cylinder arrangements for a perfecting printing operation.
Referring to FIG. 18, in each of adjacent printing cylinders, i.e., in each of first and second printing units 1 and 2, a plate cylinder 3 having a plate mounted thereon and a blanket cylinder 4 having a blanket wound thereon are arranged to be pressed against each other. A double-diameter impression cylinder 5 as an upstream cylinder with respect to the paper convey direction is in contact with the blanket cylinder 4 of the printing unit 1.
A double-diameter impression cylinder 6 as a downstream cylinder with respect to the paper convey direction is pressed against the blanket cylinder 4 of the printing unit 2. A double-diameter reversing cylinder 7 is arranged between the impression cylinders 5 and 6 to be pressed against each other.
A plurality of sets of gripper units 8 each having grippers and gripper pads and serving as a paper holding unit are aligned along the axial direction of the impression cylinder 5 at positions which divide the circumference of the impression cylinder 5 into halves. Similarly, a plurality of sets of gripper units 9 are aligned along the axial direction of the impression cylinder 6 at positions which divide the circumference of the impression cylinder 6 into halves.
Reversing gripper units 10 are aligned along the axial direction of the reversing cylinder 7 at positions which divide the circumference of the reversing cylinder 7 into halves. The positions of the reversing gripper units 10 are set to oppose the gripper units 8 and 9 upon rotation of the cylinders 5 to 7. A plurality of suction levers 11 connected to a suction air source such as a pump (not shown) are arranged near the reversing gripper units 10 at positions which divide the circumference of the reversing cylinder 7. A swinging unit 12 grips a paper sheet 15 fed onto a feeder board 14 to transfer the paper sheet 15 to the gripper unit 8 of the impression cylinder 5.
With the above structure, in single-sided printing shown in FIG. 21, when the cylinders 5 to 7 and the like are rotated, the paper sheet 15 is gripped by the gripper unit 8 and conveyed. When the paper sheet 15 passes between the blanket cylinder 4 and the impression cylinder 5, printing of the first color is performed on the paper sheet 15. The paper sheet 15 is gripped from the gripper unit 8 to the reversing gripper unit 10 which operates as in a conventional gripper unit, wound on the lower-side surface of the reversing cylinder 7, and conveyed. The paper sheet 15 wound on the reversing cylinder 7 is gripped from the reversing gripper unit 10 to the gripper unit 9 of the impression cylinder 6 and conveyed. When the paper sheet 15 passes between the blanket cylinder 4 and the impression cylinder 6, printing of the second color is performed on the same surface as in the first-color printing operation.
When such single-sided printing is to be switched to perfecting printing, the phase of the upstream cylinder group including the impression cylinder 5 with respect to the paper convey direction is adjusted such that the trailing end of the paper sheet 15 gripped by the gripper unit 8 corresponds to the suction levers 11. With this operation, the phase state shown in FIG. 21 is changed to that shown in FIG. 22. Thereafter, the printing operation is restarted. Upon rotation of the cylinders 5 to 7 and the like, the paper sheet 15 is gripped by the gripper unit 8 and conveyed. When the paper sheet 15 passes between the blanket cylinder 4 and the impression cylinder 5, printing is performed on the upper surface of the paper sheet 15. The paper sheet 15 passes through the contact point between the cylinders 5 and 7 without being gripped by the reversing gripper unit 10 at its leading end and is wound on the lower-side surface of the impression cylinder 5, as shown in FIG. 23.
When the trailing end of the paper sheet 15 wound on the impression cylinder 5 reaches the contact point between the cylinders 5 and 7, the trailing end of the paper sheet 15 is drawn by the suction levers 11 of the reversing cylinder 7 and gripped by the reversing gripper unit 10. At the same time, the leading end of the paper sheet 15 is released from the gripper unit 8. As shown in FIG. 23, the paper sheet 15 is gripped by the reversing gripper unit 10 and reversed. The paper sheet 15 is gripped from the reversing gripper unit 10 to the gripper unit 9 and conveyed by the impression cylinder 6. When the paper sheet 15 passes between the blanket cylinder 4 and the impression cylinder 6, printing is performed on the lower surface of the paper sheet 12, thereby performing perfecting printing.
The structures and operations of the suction levers 11 and the reversing gripper unit 10 will be described below in more detail with reference to FIG. 19 and 20. Gaps 7a are formed in the outer surface of the reversing cylinder 7. A plurality of grippers of each reversing gripper unit 10 axially supported to be free to pivot are arranged in each gap 7a at a predetermined interval along the axial direction of the cylinder. The grippers of each reversing gripper unit 10 are pivoted in the forward/reverse direction by a cam mechanism and a spring member (neither are shown). The grippers of each reversing gripper unit 10 are fixed on a gripper shaft 19 extending in the axial direction of the cylinder. Each reversing gripper unit 10 comprises boat-like gripper pad holders 21 having gripper pads 20 at their free end portions, and gripper holders 23 arranged next to the gripper pad holders 21 and having grippers 22 at their free end portions. Each gripper 22 provided to the gripper holder 23 is opened/closed by a cam mechanism (not shown) to grip the paper sheet 15 with the corresponding gripper pad 20.
A bearing 24 is fixed on the bottom surface of the gap 7a. A tubular suction lever shaft 25 is axially supported by the bearing 24 to be free to pivot. The suction lever shaft 25 communicates with a pump or the like through a rotary valve and is pivoted through a predetermined angle in the forward/reverse direction by a cam mechanism (not shown). The plurality of suction levers 11 are fixed to the suction lever shaft 25 in correspondence with the grippers of the reversing gripper unit 10.
The perfecting printing operation of a conventional sheet-fed rotary press with a reversing mechanism having the above structure will be described. When the reversing cylinder 7 is rotated from the state as shown in FIG. 19, a paper suction surface 11a of the suction levers 11 reaches the contact point between the cylinders 5 and 7. Immediately before the paper suction surface 11a reaches the contact point, the suction levers 11 are pivoted by the cam mechanism to a position shown in FIG. 20 and escape from the gripper pad holders 21. The reversing gripper unit 10 including the gripper pad holders 21 is largely pivoted by the cam mechanism to a position shown in FIG. 20 with a small time lag. At this time, the grippers 22 of the reversing gripper unit 10 are kept closed.
During the pivotal movement of the gripper pad holders 21, the suction levers 11 escape not to interfere with the gripper pad holders 21. After the suction levers 11 have successfully escaped from the gripper pad holders 21, the suction levers 11 return to the position shown in FIG. 19. At the same time, the rotary valve is opened, and suction air acts on the suction surface 11a of the suction levers 11. With this operation, the trailing end of the paper sheet 15 is drawn by the suction surface 11a.
The suction levers 11 which draw the trailing end of the paper sheet return to the position shown in FIG. 20 again. At the same time, the grippers 22 are opened, and the trailing end of the paper sheet drawn by the suction surface 11a of the sucker levers 11 is gripped by the reversing gripper unit 10. Thereafter, the suction levers 11 which have released the paper sheet are pivoted to the position shown in FIG. 19. At the same time, the reversing gripper unit 10 which grips the trailing end of the paper sheet conveys the paper sheet 15 in accordance with the rotation of the reversing cylinder 7. After the paper sheet 15 is gripped from the reversing gripper unit 10 to the gripper unit 9 of the impression cylinder 6, the reversing gripper unit 10 returns to the position shown in FIG. 19.
In such a conventional sheet reversing apparatus for a sheet-fed rotary press with a reversing mechanism, however, during the perfecting printing operation, the entire reversing gripper unit 10 having the grippers 22 and the gripper pads 20 is integrally moved into the gap 7a of the reversing cylinder 7 to avoid interference with the upstream impression cylinder 5. For this reason, the gripper pressure cannot be increased, and the paper sheet 15 is often gripped in an erroneous direction. Therefore, a printing failure occurs to degrade the quality of printed matter or increase wasted paper.